Implement trait TryFrom for Letter

TryFrom is implemented for '&char' instead of 'char' due to a conflict
with the blanket implementation.

For more details see:
rust-lang/rust#50133
https://old.reddit.com/r/rust/comments/c1yubv/why_this_code_does_not_compile/

Cargo.toml

@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+lazy_static = "1.4.0"

src/letter.rs

@@ -1,7 +1,66 @@
 use crate::mark::Mark;
-use std::convert;
+use std::collections::HashSet;
+use std::convert::{From, TryFrom};
 use std::fmt;
 
+lazy_static! {
+ static ref VALID_LETTERS: HashSet<char> = {
+ let mut s = HashSet::new();
+ s.insert('A');
+ s.insert('B');
+ s.insert('C');
+ s.insert('D');
+ s.insert('E');
+ s.insert('F');
+ s.insert('G');
+ s.insert('H');
+ s.insert('I');
+ s.insert('J');
+ s.insert('K');
+ s.insert('L');
+ s.insert('M');
+ s.insert('N');
+ s.insert('O');
+ s.insert('P');
+ s.insert('Q');
+ s.insert('R');
+ s.insert('S');
+ s.insert('T');
+ s.insert('U');
+ s.insert('V');
+ s.insert('W');
+ s.insert('X');
+ s.insert('Y');
+ s.insert('Z');
+ s.insert('0');
+ s.insert('1');
+ s.insert('2');
+ s.insert('3');
+ s.insert('4');
+ s.insert('5');
+ s.insert('6');
+ s.insert('7');
+ s.insert('8');
+ s.insert('9');
+ s.insert('&');
+ s.insert('\'');
+ s.insert('@');
+ s.insert(')');
+ s.insert('(');
+ s.insert(':');
+ s.insert(',');
+ s.insert('=');
+ s.insert('!');
+ s.insert('.');
+ s.insert('-');
+ s.insert('+');
+ s.insert('"');
+ s.insert('?');
+ s.insert('/');
+ s
+ };
+}
+
 pub enum Letter {
  A,
  B,
@@ -56,7 +115,6 @@ pub enum Letter {
  Slash,
 }
 
-
 impl Letter {
  pub fn str_ref(&self) -> &'static str {
  match self {
@@ -115,13 +173,11 @@ impl Letter {
  }
 
  pub fn marks(&self) -> Vec<Mark> {
- self.str_ref().chars()
- .map(|c| Mark::from(c))
- .collect()
+ self.str_ref().chars().map(|c| Mark::from(c)).collect()
  }
 }
 
-impl convert::From<char> for Letter {
+impl From<char> for Letter {
  fn from(c: char) -> Self {
  match c {
  'A' => Letter::A,
@@ -161,7 +217,7 @@ impl convert::From<char> for Letter {
  '8' => Letter::Digit8,
  '9' => Letter::Digit9,
  '&' => Letter::Ampersand,
- '\'' =>Letter::Apostrophe,
+ '\'' => Letter::Apostrophe,
  '@' => Letter::At,
  ')' => Letter::BracketClose,
  '(' => Letter::BracketOpen,
@@ -175,25 +231,35 @@ impl convert::From<char> for Letter {
  '"' => Letter::Quote,
  '?' => Letter::Query,
  '/' => Letter::Slash,
- _ => panic!("Unexpected char for Letter"),
+ _ => panic!("Unexpected char for Letter: {}", c),
+ }
+ }
+}
+
+impl TryFrom<&char> for Letter {
+ type Error = &'static str;
+
+ fn try_from(c: &char) -> Result<Self, Self::Error> {
+ println!("{}", c);
+ if VALID_LETTERS.contains(c) {
+ Ok(Letter::from(*c))
+ } else {
+ Err("Invalid char for Letter")
  }
  }
 }
 
 impl fmt::Display for Letter {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- write!(
- f,
- "{}",
- self.str_ref()
- )
+ write!(f, "{}", self.str_ref())
  }
 }
 
 #[cfg(test)]
 mod test {
- use super::Letter;
+ use super::{Letter,VALID_LETTERS};
  use crate::mark::Mark;
+ use std::convert::{From, TryFrom};
 
  #[test]
  #[should_panic]
@@ -215,22 +281,22 @@ mod test {
 
  #[test]
  #[allow(non_snake_case)]
- fn convert_M() {
+ fn from_M() {
  assert_eq!(Letter::from('M').to_string(), "--");
  }
 
  #[test]
- fn convert_0() {
+ fn from_0() {
  assert_eq!(Letter::from('0').to_string(), "-----");
  }
 
  #[test]
- fn convert_period() {
+ fn from_period() {
  assert_eq!(Letter::from('.').to_string(), ".-.-.-");
  }
 
  #[test]
- fn convert_apostrophe() {
+ fn from_apostrophe() {
  assert_eq!(Letter::from('\'').to_string(), ".----.");
  }
 
@@ -239,4 +305,21 @@ mod test {
  assert_eq!(Letter::M.marks(), vec![Mark::Dash, Mark::Dash]);
  }
 
+ #[test]
+ #[allow(non_snake_case)]
+ fn try_from_M() {
+ assert_eq!(Letter::try_from('M').unwrap().to_string(), "--");
+ }
+
+ #[test]
+ fn valid_char() {
+ assert!(VALID_LETTERS.contains(&'M'));
+ assert!(!VALID_LETTERS.contains(&'m'));
+ assert!(!VALID_LETTERS.contains(&' '));
+ }
+
+ #[test]
+ fn try_from_m() {
+ assert!(Letter::try_from(&'m').is_err());
+ }
 }

src/lib.rs

@@ -1,2 +1,5 @@
+#[macro_use]
+extern crate lazy_static;
+
 pub mod letter;
 pub mod mark;